Various types of traffic lane marking systems are shown in different U.S. Patents. Some use active markers, meaning markers that emit a signal of some sort, while others use passive ones.
For example, U.S. Pat. No. 5,347,456 describes a system of passive markers that are placed along a centerline of a traffic lane and contain coded information that can be read by a vehicle traveling over them.
Other types use on-board cameras and imaging techniques to acquire roadway information, process the acquired information, and then relate the vehicle to the processed roadway information. Those types of systems would seem to be quite complex and very expensive for widespread use in mass-produced motor vehicles, especially if the information must be acquired and processed in real time. U.S. Pat. Nos. 6,614,469 and 6,411,901 are examples of such systems.
Still another patented system uses GPS to relate a traveling vehicle to stored data defining lane boundaries.
U.S. Pat. No. 6,502,031 proposes the use of magnetic markers in a roadway for detection by suitable on-board equipment.
U.S. Pat. No. 6,414,606 proposes the addition of metallic shot or particles of other materials having a high dielectric constant to a thermoplastic paint used to paint lane stripes on pavement. A vehicle containing suitable detection equipment can detect the additive material in the painted stripes.